Solvent extraction of unsaturated materials



@ntented fiaprt 22 2-} SOLVENT EXTRACTION OF MATERIALS Johan C. D.Oosterhout and Thomas C. Roddy,- Jr., Port Arthur, Tex., assignors toThe Texas Company, New York, N. Y., a. corporation of Delaware NoDrawing. Application March 1, 1945,

Serial No. 580,482

This invention relates to the solvent extraction of unsaturatedmaterials and particularly the extraction or extractive distillation ofhydrocarbons containing mono-olefins or di-oleflns, 'or both. withfurfural or a furan type of compound.

The invention has to do with employing the solvent, namely furfural, inthe presence of an agent adapted to inhibit polymer formation during theextractive treatment and during recovery of the solvent from thehydrocarbons.

More specifically, the invention contemplates employing furfural as anextraction solvent in the presence of a small amount of a compoundhaving at least one phenylamino group and selected from the group 01'compounds consisting of N-phenyl substituted guanidines, naphthylaminesand thioureas. Compounds which have been found effective are a, N-phenylnaphthylamine, N,N'-diphenyl guanidine and N,N-diphenyl thiourea. Theterm N-phenyl is intended to mean that phenyl is substituted onnitrogen.

These compounds are efiectlve in stabilizing furfural at elevatedtemperatures and are efiective in inhibiting polymer formation.

Furfural is a useful solvent for efi'ecting fractional separationbetween olefinic and parailin hydrocarbons and also for effectingseparation between oleflns differing in degree of unsaturation. Thus, itmay be used for eflecting separation between mono-olefins anddi-olefins;

It has been found that when furfural is used to extract unsaturates suchas butadlene from hydrocarbon mixtures the furfural becomes contaminatedduring continued use with a. small but appreciable amount of polymer orresin material. The mechanism of this polymer formation is not entirelyclear. It may be that furfuraiunder the conditions employed during theextractive treatment or during its recovery from the hydrocarbonsundergoes polymerization to a small extent, or may enter into reactionwith olefinlc hydrocarbons forming polymer material, or both of thesereactions may take place. Also, the unsaturated hydrocarbons may undergopolymerization in the presence of the furfural.

Th presence of this polymer material in the mixture of hydrocarbons andfurfural is objectionable because it forms deposits within the plantapparatus and particularly the distillation, heat exchange and otherapparatus used for recovering the furfural. It tends to stick to themetal surfaces and as a. result during continued exposure to elevatedtemperatures is converted into solid carbonaceous form. The depositionof this material upon the surfaces of the heat. exchangers interfereswith their emcient operation and in addition results in the necessityfor frequent cleaning of the apparatus. This deposition may be soserious as to cause a shutdown of the plant.

The present invention,- therefore, involves effecting the extraction ofcleflnic or otherunsatu;

. rated hydrocarbons from mixtures containing them with'furfural in thepresence of an inhibitor selected from the foregoing group of compounds.

The inhibitor is maintained present in the solvent in amounts of about0.1 to 0.2% or inamounts ranging from about 0.01 to 0.1% by weight ofthe furi'ural. added initially to the solvent or may be addedperiodically or continuously in amounts necessary to malntainthe desiredconcentration in the solvent.

In accordance with the invention wherein it is desired to extractbutadiene from a C4 hydrocarbon mixture by extraction or extractivedistillation, the hydrocarbon mixture is subjected to contact withfurfural in the presence of the inhlbitor at temperatures in the rangeabout to 840 B. so as to produce an extract phase comprising furfuraland dissolved butadlene. This extract phase is separately subjected todistillation, advantageously in the absence of steam, so as to strip thehydrocarbons from the solvent at temperatures in the range about 280 to340 F.

Conventional apparatus and procedure may be employed in carrying out thesolvent extraction or extractive distillation of hydrocarbons or otherliquid mixtures and therefore a detailed description is unnecessary,

The foregoing inhibitors exert a, stabilizing effect upon the solvent inthe absence of the unsa turated hydrocarbons so that they are useful instabilizing the solvent where it is being retained in storage or supplytanks for appreciable periods of time at temperatures substantiallyabove atmospheric. For example, a sample of iurfural which wassubstantially water-white in color and contained no inhibitor wassubjected to a tem- The inhibitor may be' of inhibitor per 1,000 barrelsof furfural, after 15 to 20 minutes exposure at about 300 F. remainsunchanged. This is to be contrasted with furfural containing certainother types of compounds, such as 2,6-dibutyl-4-methyl phenol,

alpha hydroxy-isobuty-rio acid, which darkens perceptibly in 15 to 20minutes time. The sample containing the phenol compound darkened con;-siderably even at a temperature not in excess of about 120 F.

By way of additional examples, a,N-phenyl naphthylamine, N,N'-diphenylguanidine and N,N-diphenyi thiourea were added to separate quantities offreshly distilled furfural which was substantially water-white in color.The inhibitors were added in the proportion of about 400 pounds ofinhibitor per 1,000 barrels of "furfural' which is equal to 0.1% byweight of the furfuralf The furfural containing these inhibitors wasmaintained at a temperature of about 315 to 320 F. in an oil bath in thesubstantial absence of an oxidizing atmosphere. The following tabulationindicates the comparative activity of the three compounds in inhibitingcolor formation over a prolonged period of time.

Development of color in inhibited jurlura l Hours From a, henylN,N'-diphenyl N,N-dlphenyl Start Napht ylaminc Guanidine Thiourea lWater-White Water-White..-- Water-White V e r y L ig h t Slight Slight.

Brow-n. LightBrownnh Very Light Very Light Brown. Brown. 0 .-do LightBrown.-. Light Brown. 8...- an DO.

Brow While the foregoing examples show the utility of the compoundsinquestion for stabilizing furfural at elevated temperatures,nevertheless it is contemplated that these compounds may be used forstabilizing other solvents of the furan type, such as furfuryl alcoholand tetrahydrofurfuryl alcohol. Accordingly, in the appended claimsfurfural is used in a comprehensive sense to include solvents of thefuran type.

Also, while mention has been made of using the invention in conjunctionwith the solvent extraction of mixtures containing olefinic hyshould beimposed as are indicated in the appended claims. We claim:

1. The method of extracting olefins from an oleflnic hydrocarbon mixturewhich comprises extracting said hydrocarbon mixture containinmono-olefins and di-olefins with furfural at elevated temperatures inthe presence of a small amount of a compound having, at least onephenylamino group and selected from the group of compounds consisting ofN-phenyl substituted thioureas, guanidines and naphthylaminessufilcient' to inhibit substantial polymer formation, forming a solventphase containing dissolved oleflns and a'hydrocarbon phase comprisingrelatively insoluble hydrocarbons, separating said phases, and removingsolvent from the hydrocarbons.

2. The method of extracting. oleflns from an olefinic hydrocarbonmixture which comprises extracting. said hydrocarbon mixture containingmono-olefins ,and di-olefins with furfural at a temperature in the rangeabout 140 to 340 F. in the presence of a small amount of a compoundhaving at least one phenylamino group and selected from the group ofcompounds consisting of N-phenyl substituted thioureas, guanidines andnaphthylamine sufiicient to inhibit substantial polymer formation,forming a solvent phase con-.

taining dissolved olefins and a hydrocarbon phase comprising relativelyinsoluble hydrocarbons, separating said phases, and removing solventfrom the hydrocarbons.

3. The method of extracting butadiene from a C4 hydrocarbon mixturecontaining butadiene.

and including mono-olefins which comprises extracting said mixture withfurfural at a. tem-- perature in the range of about 140-340 F.lIl.

' the presence of a small amount of N,N'-diphenyl thiourea, saidthiourea compound amounting to about 0.1 to 0.2 per cent by weight ofthe furfural,

forming a solvent phase comprising butadiene dissolved in furfural and ahydrocarbon phase comprising relatively insoluble hydrocarbons;

separating said phases and removing furfural from the hydrocarbons.

, JOI-LAN C. D. OOSTERI-IOUT.

THOMAS C. RODDY, JR.

' REFERENCES- crrnn Thefollowing references are of record in the file ofthis patent:

UNITED STATES- PATENTS Number Name Date 2,080,142 Lowry et a1. May 11,1937 2,087,455 Stratford July 20, 1937 2,349,473 Tannich May 23, 19442,350,609 Hachmuth June 6, 1944 2,247,926 Smith July 1, 1941 2,294,972Figg et al Sept. 8, 1942 2 341.874

Lovell Feb. 15, 1944

